The document highlighted Osborne's early opposition to the nationalisation of Northern Rock and Bradford & Bingley, his support for a Tory report advocating the deregulation of the mortgage market, and his pledges on fuel duty and hospital beds.

The Conservatives hit back, accusing Labour of an attempt to distract attention from its own failings.

Labour is seeking to pile pressure on the shadow chancellor, who has come under intense pressure over his meetings with Russian oligarch Oleg Deripaska. His poll rating has also slipped, with Osborne trailing behind Alistair Darling, the chancellor, on who is most trusted to handle the economy.

The Labour party claimed Tory plans for 45,000 new single rooms in NHS hospitals were based on "back of the envelope" calculations that put the bill at £1.57bn, when Department of Health estimates - released this week in response to a Conservative parliamentary question - calculated it at more than £9.5bn.

Stephen Timms, the financial secretary to the Treasury, said that the Tory figure was extrapolated from the bill for 81 recent single-room conversions, which were more "straightforward and cost-effective" than would be the case in most NHS hospitals.

The £8bn discrepancy gave the lie to Osborne's claim that Tory plans were "fully costed", said Timms.

Echoing Gordon Brown's speech to the Labour party conference, the dossier said: "George Osborne's schoolboy errors and lack of judgment show why this is no time for a novice."

Timms said: "Whenever George Osborne has faced a tough test, his judgment has been shown to be wrong. He has shown a willingness to create headlines on the hoof without care for the consequences.

"Nowhere is this clearer than in his pledge on single rooms, which won good headlines but would require an extra £8bn in health service funding for which George Osborne has failed to budget.

"Labour is steadily increasing the proportion of single rooms in the NHS, but we have to do this on an affordable and responsible basis."

The Conservatives dismissed the claims, saying: "This is just an attempt to draw away from the fact that the economy is in a shockingly weak state and the government is without a clue on how to remedy matters. Labour will leave this country with the biggest overdraft in history and they do not know how to undo the damage so they are spending their time drawing up daft dossiers instead."

The Department of Health was asked for calculations on the cost of building 45,000 single NHS rooms by Mark Hoban, a member of the Conservatives' shadow Treasury team.

The Conservatives estimated the cost of building the rooms would be £35,000 a bed, equivalent to £1.57bn in total.

But a written answer from Ann Keen, the junior health minister, published on Tuesday, said DoH officials estimated that the cost would be £211,401 per bed, equivalent to £9.51bn.

Keen said in her answer: "NHS organisations make decisions locally based on practical considerations such as site restrictions, affordability, as well as clinical and operational limitations. Any national estimate must therefore make assumptions regarding the methods likely to be used for providing more single rooms and the likely cost effects of such methods."

The Conservatives insisted today they were "absolutely confident" of their original calculations.

Andrew Lansley, the Tory health spokesman, announced last month that by the end of a first Tory term in office single NHS rooms would be available for all expectant mothers, mental health patients and anyone undergoing an operation.

A Tory spokesman said: "To achieve our goal of offering any NHS patient who wants one a single room we need to dramatically increase the number of single rooms within the NHS. The vast majority of the cost of doing this will be provided by converting existing wards. The cost of this is massively less expensive than the government is now claiming. And so we are absolutely confident of our original costings."

Labour's wide-ranging dossier on Osborne also points out that the Conservatives' proposed fuel duty escalator, unveiled with great fanfare in July, would mean motorists paying 5p a litre more in tax on petrol now.

This is because the escalator is based on the principle that tax falls as the cost of fuel goes up and rises when it comes down, it would have saved drivers 5p a litre when pump prices were £1.18 in the summer, but cost them a similar amount in extra tax now that they have dropped to 98p, said Labour.

In a further attempt to embarrass the Conservatives, the dossier highlighted a comment made by Osborne in the House of Commons in February in which he stated he was "not in favour of nationalisation, full stop" for Northern Rock.

Labour claims the shadow chancellor's opposition to provisions in the banking bill would have stood in the way of the government taking the ailing bank and part of Bradford & Bingley into public ownership.

The dossier also drew on the fact that Osborne welcomed last year's Conservative economic competitiveness policy group report, which advocated deregulation of the mortgage market, hailing it in his conference speech in October 2007 as the first signs of global economic turmoil were emerging.

It also quotes the shadow chancellor's description of the short-selling that was blamed for heightening the difficulties faced by banks like Bradford & Bingley as "a function of capitalist markets".